This application is concerned with combining electrophysiological and ultrastructural techniques in the study of: (a) retinal synapses, and (b) cell-to-cell communication in the lens. The first project includes: (1) an analysis of the mechanism of transmitter release and synaptic vesicle membrane recycling in retinal photoreceptors, using rapid freezing at 4 degrees K, freeze-fracturing and ultrastructural tracer techniques; (2) a study of the connectivity of the different functional types of bipolar cells in a mammalian retina. Furthermore, (3) the possibility will be explored that functionally active bipolar cell endings could be identified by ultrastructural tracer techniques. The second project is a study of metabolic cooperation in the lens via gap junctions using electron microscopy, intracellular recording technique, tissue culture and biochemistry.